英语听力：自然百科 澳大利亚大堡礁 Great Barrier Reef—2

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Life doesn't just reside here. The reef itself is built by one of its smallest tenants⁵. 

 

For more than 15 years, marine⁶ scientist Dave Wachenfeld has been coming down here to study coral polyps. These tiny creatures are closely related to jellyfish, but much smaller. They don't have a bone in their body. 

 

Yet for half a billion years, they've been nature's greatest builders, architects of labyrinths⁷ of limestone⁸. 

 

Wachenfeld: “When we look at the surface of these soft corals, we can see the hundreds of tiny polyps.” 

 

Every bit of this reef has had an odyssey⁹ to get here. The coral starts out life as larvae¹⁰, floating free in the ocean. For each one, the chances of survival are slim.

 

They have to run the gauntlet of a million hungry mouths as they cross up to 1000 miles of open ocean. Fewer than one in 100,000 complete the journey.

 

And then they’re faced with a second hurdle--finding the perfect landing site. Falling on sand or a crowded outcrop is death. Those precious few that survive will start a colony. Once settled, the larvae begin to grow. Transforming into adults called polyps. They develop tentacles¹¹ that can grab food from the water.

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